Improving the safety of the furnace in our school building (Activity Report)

WHEN THE TECHNICIANS from the Gas Company came to restore service after the fumigation was completed, they red-tagged our school building’s furnace as having a safety issue, due to the closet that houses it. Namely, they perceived two ways that post-combustion exhaust gases from the furnace just might get sucked by the blower into the air that is circulated through the building, rather than being vented up above the roof.  

A gas company technician explains the problems.

Honestly, the hazard did seem pretty unlikely to me, given the configuration of equipment. Yet Fleming and I took the recommendations seriously, especially for the sake of our preschool. The resolution seemed simple if we could find the right person to handle it. So we made some inquiries—and within 6 working days the problems were fixed, for about $150. 

Below the jump, this post documents the two suspected problems, as well as their resolution. I created this post because given normal wear-and-tear, these apparent hazards will eventually appear again—and will need attention in the future. 

Diagnosis

1.  Because there is only one return register in the system, it creates a relatively powerful suction. And because it is located directly below the furnace closet, it could create a downdraft that pulls combustion gases from the furnace through the closet doorway. Therefore the doorway needed to be made airtight.

2.  The narrow top-hinged doorway to the chamber that holds the furnace filter was not closing all the way. That opening could likewise create a downdraft that pulls combustion gases from the furnace into the slot opening. Therefore the door needed to be made airtight.

(This episode has shaken my confidence in the HVAC contractor that has been coming to do semiannual maintenance on our system for years—and yet apparently didn’t notice these safety issues.)

Resolution

I called a state-licensed insulation contractor named Koala Insulation (apparently a national franchise). Although our job was too small for them to undertake formally, a fellow on their staff offered to do it as a side job. Apparently Giovanni does weatherstripping as part of his regular work—which meant that he knew what materials were needed and how to apply them—and he was available the same week. It took him and his buddy about an hour.

The newly weatherstripped door
looks much the same at first glance.

A black rubber sweep attached along the bottom 

has filled in the gap below the door.

A narrow strip of white foam around the frame
creates an airtight seal.

A strip of gray foam along the bottom edge
now closes the air gap at the filter chamber’s door.

I added duct tape along the hinge of the filter door,
to prevent air flow around the hinge.